Off-site BNG explained

Most developments in England have to deliver a 10% biodiversity net gain. Where that gain cannot be delivered on the development site, it can be bought as units from a habitat bank somewhere else. That is off-site BNG. It is often written “offsite BNG”, and it is the part of the system we deal in.

This post sets out how it works, so the term stops being a black box on a planning officer’s report.

What off-site BNG means

The statutory biodiversity metric scores your site before and after development. If the after figure is not at least 10% above the before figure, there is a shortfall, measured in biodiversity units. Off-site BNG means closing that shortfall with units generated on land that is not your development site.

The units come from habitat that a landowner has created or enhanced and legally committed to manage for at least thirty years. That land is a habitat bank. When you buy units, the bank’s gain is allocated to your development on the national biodiversity gain sites register, and your planning authority accepts that allocation as evidence in your biodiversity gain plan.

When you can use it

The biodiversity gain hierarchy expects on-site delivery to be considered first. What that means in practice depends on the size of the scheme.

• Minor developments. Since 6 August 2026, minor developments no longer have to show that on-site delivery is not feasible before looking off site. On-site and registered off-site units can be considered side by side, so a small scheme can go straight to buying units.
• Major developments. The full hierarchy still applies. On-site delivery has to be properly tested first, and the off-site units cover what remains.

Statutory biodiversity credits, bought from the government, sit below both options. They are deliberately priced well above the private market so they act as a backstop, and they are rarely the right answer.

Where the units come from

A habitat bank is secured through a section 106 agreement with the local authority or a conservation covenant with a responsible body. Either one locks the land into a management plan for at least thirty years. Progress is evaluated by the authority or the responsible body, and enforcement runs against whoever entered the agreement.

That is the point of buying off site. Once your units are allocated and your gain plan is approved, the obligation is discharged. The thirty-year duty to create, manage, monitor and report sits with the bank, not with you. The developers page goes into what that is worth.

How many units you need

Two things in the metric decide how many units your shortfall translates into, and both affect the price more than the headline rate per unit.

The spatial risk multiplier. Units from a bank in the same local planning authority or National Character Area as your site count at full value. Units from further away are discounted, so you need more of them. A bank two counties away can cost more in total than a dearer one nearby. There is more on this in Where your units come from changes how many you need.

The trading rules. Area habitats, hedgerows and watercourses are measured separately and cannot be swapped for one another. Within area habitats, the loss of a distinctive habitat generally has to be replaced with something of the same or higher distinctiveness. Trading up, replacing a loss with habitat of higher distinctiveness, is allowed, and it sometimes opens a cheaper or quicker route.

What buying looks like

The process is shorter than most people expect once someone owns it.

1. Enquiry. You send your completed metric, or a site location and a red-line plan if you are earlier than that.
2. Assessment. An ecologist checks the requirement against what is available: habitat types, distinctiveness, trading rules and the spatial multiplier.
3. Written quote. Unit types and quantities, the multiplier applied, the price per unit and the total. Ours hold for three months.
4. Reservation, if you want it. Specific units are held while your application is determined, against a deposit that comes off the final price. The deposit is not refundable, so the period is set against a realistic view of your timetable.
5. Allocation. The sale completes, the units are allocated to your development on the register, and you receive the evidence your planning authority asks for.

The buyer still files their own biodiversity gain plan with the authority. We help complete it and update the metric, and we handle the coordination between the bank, the landowner, the authority and any responsible body. How it works has each stage in detail.

Two things worth knowing before you start

Supply is uneven. Some areas have plenty of units and some have very few, and the habitat types that are scarce are the ones most likely to be gone by the time a decision comes through. Prices move too, and not always downwards. A quote you can hold, and a reservation while planning is determined, are the answer to both.

And the metric you submit is fixed. Nobody can change it once it is with the authority. The savings on off-site BNG come from being involved before that point, when the layout can still reduce what is lost.

If you have a shortfall to close, send us the metric and we will come back with a number.